A fluorine-containing polymeric polyformals is described which has the repeating unit O CH2 O CH2 (CF2) sub n CH2 wherein n is an integer of from about 3 to about 6 prepared by reacting trioxane with a diol having the formula HO CH2 (CF2) sub n CH2 OH. These polymeric polyformals are useful directly for impervious coatings on metals and the like.